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Lewis-McKenzie polygraph, made in 1900 by Cambridge and Paul Instrument Co. This device was used to graphically record venous and arterial pulses simultaneously. One tube is placed on the jugular vein (neck) and the other on the brachial artery (arm) the two tambours register the pulses of each and the mounted pens would register a graphical trace of each on a continuous roll of paper. The polygraph was widely used to diagnose arrhythmias.
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